1. Field of the Invention
The present invention relates generally to enhancing safety in the use of breathing systems.
2. Background Discussion
Conventional breathing systems, such as systems used for underwater diving situations, mining, firefighting or outer space, typically provide a gas supply system to a user who is underwater, or in another oxygen-depleted or toxic gas environment. These systems are typically portable and are adapted to provide sustained usable air for breathing for an estimated period of time.
Examples include AQUA-LUNG® or SCUBA (Self Contained Underwater Breathing Apparatus), which is used by free divers and, in similar fashion, by fire fighters in many hazardous situations. Typically, a SCUBA-type apparatus employs a relatively large tank containing a compressed gas mixture and a mouthpiece or face mask connected to the tank through a flow regulator. The gas mixture commonly consists of two or more constituent gases, such as oxygen and one or more inert gases such as nitrogen. A user inhales from the tank and exhales into the ambient atmosphere.
Another type of apparatus, a rebreathing apparatus, has been developed to recycle gases exhaled by a user to remove carbon dioxide therefrom with a “scrubber” and then recycle the unmetabolized oxygen. Oxygen or an oxygen-enriched gas mixture is injected into the “scrubbed” gas from a supply source to maintain the partial pressure of oxygen in the gas mixture at a desired level, and then the gas mixture is passed back to the user for rebreathing. Rebreathers can therefore extend the amount of time the breathing device can be used by lowering the rate of consumption of the gas mixture.
Pure oxygen is often utilized in rebreathers, introducing the problem of hyperoxia, which is excess oxygen in body tissues caused by breathing oxygen at elevated partial pressures or oxygen-rich gases at normal atmospheric pressure for a prolonged period of time. Hyperoxia can cause cell damage in the central nervous system and the lungs of a user.
Early rebreather systems were relegated to use by professionals in unsafe environmental conditions, such as diving or firefighting, due to the complexity and costs of the systems as well as the extensive training required for the use of these systems. These systems exhibited an undesirable level of control over partial pressure of oxygen (PPoxygen) in the gas mixture present in the rebreather system, potentially resulting in a user experiencing hyperoxia or hypoxia, which is oxygen deprivation capable of causing loss of consciousness, seizures, coma, priapism or death. An increase or decrease in PPoxygen in a rebreather can result in a hyperoxic or hypoxic gas detrimental to the rebreather user.
Because of the dangers posed by hyperoxia and hypoxia, it is essential for the diver to monitor and have accurate data for PPoxygen for the duration of a dive. Currently-available rebreather systems incorporate sensors, processors and indicators to detect, measure, control and display PPoxygen continuously during a dive. However, the sensors used in these systems, while improved over early rebreather systems, are still prone to malfunctions, rendering the systems less reliable than desired for maintaining target oxygen levels. Often, the problem of malfunctioning sensors is not resolved even by incorporating redundant sensors in the rebreather and utilizing a protocol implemented by the processor to identify whether one or more of the sensors is not operating correctly.
Methods and protocols known in the art are directed to monitoring oxygen levels during a dive. For the foregoing reasons, there is a need for an apparatus and method that may be used by a diver prior to undertaking a dive in order to confirm proper functioning of the rebreather sensors and processor.